Various mechanical shock machines are known, which develop G forces by the controlled collision of a hammer and anvil system. Various interface materials may be used to modify the duration and shape of the shock induced by the collision. Usually the device or component to be tested is mounted on the moving or hammer part, although the opposite may be true where severe shock levels are required.
However, most mechanical shock generating machines produce secondary physical stimuli such as damped vibration, secondary shocks and off-axis motion, which, of course, is highly undesirable. This is particularly true where shock levels above 500 G's are required and such undesirable vibrations may damage the device under test.
A G is equal to 978 cm/sec.sup.2 at 0 degrees latitude. Thus, a G is defined as the acceleration due to the gravity on earth.
Furthermore, the physical impact associated with the shock pulse generated by the machine may cause injury to personnel if the machine is not properly protected by shields or electronic safety devices. This is particularly true because the impact occurs in many cases in a location accessible to an operator. An example of such a shock generating machine is shown in the U.S. patent to Otera, et al., No. 3,597,960. This machine will generate shocks on the order of 4,000 G's.
It should also be noted that, typically, mechanical shock machines are made with special accelerometers to measure such shocks. A controversy has been generated concerning the propriety of electronically filtering higher frequency components of the shock pulses. This will cause the shaped mechanical pulse to look "clean" even though, in fact, the device under test may be subjected to severe secondary stimuli.